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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 69 |
| 5 | 246 |
| 6 | 896 |
| 7 | 3312 |
| 8 | 12371 |
| 9 | 46582 |
| 10 | 176528 |
| 11 | 672464 |
| 12 | 2572700 |
| 13 | 9878116 |
| 14 | 38044450 |
| 15 | 146911680 |
| 16 | 568617615 |
| 17 | 2205268306 |
| 18 | 8567986878 |
| 19 | 33341710740 |
| 20 | 129932332749 |
| 21 | 506997589626 |
| 22 | 1980621229040 |
| 23 | 7745660095820 |
| 24 | 30320567651424 |
[1,2,6,20,69,246,896,3312,12371,46582,176528, 672464,2572700,9878116,38044450,146911680, 568617615,2205268306,8567986878,33341710740, 129932332749,506997589626,1980621229040, 7745660095820,30320567651424] |